It isn't possible to simply calculate it, knowing only the densities of the two pure elements. Each compound can form crystals, sometimes many different kinds of crystals, and each will have its own density.

and you dont know about the other question??
((to creat a film of alloy Al and Ti we use to flux of each element and a substrat.
if the flux of Al is double of that of Ti, then we obtain an alloy on the substrat AlTi or what???))

Also almost impossible to answer. What kind of film you end up will depend on many different parameters (including deposition parameters such as temperature, pressure etc). My guess would be that you would end up with a granular film with grains of Al and Ti (Al tends to form small grains so the film might even be quite dense).
But again, that is only a guess.
In order to calculate something like that you would need a reasonably good supercomputer and extensive knowledge of DFT calculations